Efficiency monitor for inductive power transmission

ABSTRACT

An efficiency monitor for monitoring the efficiency of power transmission by an inductive power outlet. The efficiency monitor includes an input power monitor, for measuring the input power delivered to the primary coil, and an output power monitor, for measuring the output power received by the secondary coil. The input and output powers are used by a processor to determine an index of power-loss. A circuit breaker may be used to disconnect the inductive power outlet in case of excessive power loss.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/563,558 filedSep. 21, 2009, which is a continuation of PCT application Serial No.PCT/IL2008/000401 filed Mar. 23, 2008, which claims the benefit of U.S.provisional application Ser. Nos. 60/907,132 filed Mar. 22, 2007,60/935,847 filed Sep. 4, 2007, 61/006,076 filed Dec. 18, 2007,61/006,106 filed Dec. 19, 2007, 61/006,488 filed Jan. 16, 2008 and61/006,721 filed Jan. 29, 2008, the disclosures of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a system and method for monitoringefficiency and controlling power transfer across an inductive powercoupling.

BACKGROUND

For safety, the power supplying side of a conductive couple is generallythe female part, and does not have bare conductive elements protrudingtherefrom. A plug coupled to the device is the corresponding male partwith bare pins. The size of the pins and holes are such that a childcannot insert his or her fingers thereinto. In high quality sockets, anearth connection is provided, and, only when a plug with a longer earthpin is inserted thereinto, is it possible to insert a pin (or anythingelse) into the holes connected to the current carrying live and neutralwires. Nevertheless, socket holes are dangerous and children dosometimes manage to insert pencils, pins and other objects into socketholes, sometimes with fatal results. Water can also cause shorting andmay result in electrocution.

It can therefore be safer and more reliable to provide socket-less poweroutlets such as inductive couplers. Inductive power coupling allowsenergy to be transferred from a power supply to an electric load withoutconnecting wires. A power supply is wired to a primary coil and anoscillating electric potential is applied across the primary coil whichinduces an oscillating magnetic field therearound. The oscillatingmagnetic field may induce an oscillating electrical current in asecondary coil, placed close to the primary coil. In this way,electrical energy may be transmitted from the primary coil to thesecondary coil by electromagnetic induction without the two coils beingconductively connected. When electrical energy is transferredinductively from a primary coil to a secondary coil, the pair are saidto be inductively coupled. An electric load wired in series with such asecondary coil may draw energy from the power source when the secondarycoil is inductively coupled to the primary coil.

Low power inductive electrical power transmission systems over extendedsurfaces are not new. One such example is described in U.S. Pat. No.7,164,255 to Hui. In Hui's system a planar inductive battery chargingsystem is designed to enable electronic devices to be recharged. Thesystem includes a planar charging module having a charging surface onwhich a device to be recharged is placed. Within the charging module,and parallel to the charging surface, at least one, and preferably anarray of primary windings are provided. These couple energy inductivelyto a secondary winding formed in the device to be recharged. Suchsystems are adequate for charging batteries in that they typicallyprovide a relatively low power inductive coupling. It will beappreciated however, that extended base units such as Hui's chargingsurface which transmit energy continually approximately uniformly overthe whole area of the unit, are not suitable for use with high energysystems.

By not requiring holes for coupling pins, socket-less outlets may bedisguised more effectively than conductive sockets, and are thus lessobtrusive. A primary inductive coil, for example, may be concealedbehind a surface. Generally, the fact that socket-less outlets are lessobtrusive is advantageous. But being harder to spot than conventionalpower outlets has its disadvantages. The user must somehow locate theoutlet before being able to use it by bringing a secondary coil intoproximity therewith. The problem of locating such sockets isparticularly acute where the power outlets are behind a concealingsurface such as a desk top or wall, and the positions thereof areadjustable over a large area.

Locating mobile source ‘hotspots’ or sockets is particularly problematicin high power systems where no extended power transmission surface isprovided. Moreover, a high power primary coil produces a largeoscillating magnetic field. Where a secondary coil is inductivelycoupled to the primary coil, the resulting flux linkage causes power tobe drawn into the secondary coil. Where there is no secondary coil tofocus the power, the oscillating magnetic field causes high energyelectromagnetic waves to be transmitted which may be harmful tobystanders. In contrast to low power systems, such as Hui's chargingsurface, where excess heat may be readily dissipated, uncoupled highpower primary coils and their surroundings may become dangerously hot.

In order to provide power to electrical devices in an efficient mannerit is important that certain parameters of the power are regulated. Byfeeding back such parameters as working voltage, current, temperatureand the like, the power supply to an electric device may be optimized tominimize energy losses and to prevent excessive heating of thecomponents. Consequently, it may be useful to provide a signal transferchannel for power regulation and the like. Thus a communication channelbetween source and load device is often provided alongside the powerinput channel in conventional conductive power supply systems. Methodsfor providing such a communication channel include wired connections tothe device that are often packaged in the same cable as the power linesand conductively coupled to the load via conventional pin-and-sockettype connectors.

Leak prevention systems which are able to detect power emanating from aprimary coil of an inductive power source and to cut off power to theprimary coil if no secondary coil is coupled thereto have beenconsidered. However in order to prevent power leakage from a primarycoil while a secondary coil is coupled thereto, a communication channelbetween the secondary and primary coil would be useful. Nevertheless dueto the lack of connecting wires in inductive power couplings, conductivecommunication channels are not practical.

There is a need for a control system for inductive power outlets, whichis capable of locating a concealed power outlet, preventing powerleakage from the power outlet, locating secondary coils close to thepower outlet and regulating power transfer from the power outlet to asecondary coil coupled thereto. The present invention addresses thisneed.

SUMMARY OF THE INVENTION

A first aspect of the invention is directed to providing signal transfersystem for controlling power transfer across an inductive powercoupling, said inductive power coupling comprising a primary inductivecoil wired to a power source and a secondary inductive coil wired to anelectric load; said system comprising:

a. at least one signal generator for generating a control signal;

b. at least one transmitter for transmitting said control signal, and

c. at least one receiver for receiving said control signal.

Optionally and preferably, the control signal for carrying encoded datapertains to at least one of the group comprising:

d. presence of said electric load;

e. location of said primary inductive coil;

f. location of said secondary inductive coil;

g. required operating voltage for said electric load;

h. required operating current for said electric load;

i. required operating temperature for said electric load;

j. required operating power for said electric load;

k. measured operating voltage for said electric load;

l. measured operating current for said electric load;

m. measured operating temperature for said electric load;

n. measured operating power for said electric load;

o. power delivered to said primary inductive coil;

p. power received by said secondary inductive coil, and a useridentification code.

In one embodiment, the signal generator comprises a transmission circuitconnected to the secondary inductive coil; the transmitter comprisingthe secondary inductive coil, and the receiver comprising the primaryinductive coil connected to a reception circuit wherein: saidtransmission circuit comprises an ancillary load selectively connectableto said secondary inductive coil, and said reception circuit comprisesat least one power monitor for monitoring power provided to said primaryinductive coil.

In one embodiment, the transmission circuit further comprises at leastone switching unit comprising: a modulator for modulating a bit-ratesignal with an input signal to create a modulated signal; and a switchfor intermittently connecting said ancillary load to said secondaryinductive coil according to said modulated signal, and said receptioncircuit further comprises: at least one current monitor for monitoring aprimary current drawn by said primary inductive coil, thereby producinga primary current signal, and at least one correlator forcross-correlating said primary current signal with said bit-rate signal,thereby producing an output signal.

The signal transfer system may be further characterized by at least oneof the following restrictions:

-   -   said switching unit further comprises a controller configured to        encode data into said input signal;    -   said switching unit further comprises a frequency divider;    -   said inductive power coupling transfers energy with a driving        frequency and said bit rate frequency is an integer fraction of        said driving frequency;    -   said inductive power coupling is a device selected from the        group comprising: a transformer, a DC-to-DC converter, an        AC-to-DC converter, an AC-to-AC converter, a flyback        transformer, a flyback converter, a full-bridge converter, a        half-bridge converter and a forward converter; and    -   said primary inductive coil is galvanically isolated from said        secondary inductive coil.

In another embodiment, the transmission circuit further comprises ahalf-wave rectifier, and the reception circuit is configured to detectsecond harmonic signals in the power supplied to said primary inductivecoil when said secondary inductive coil is coupled thereto.

Optionally, a plurality of the primary inductive coils are eachconnected to a driver and the driver is configured to selectivelyoperate each primary inductive coil in turn so as to identify whichprimary inductive coil is closest to the secondary inductive coil.

Optionally, each primary inductive coil is operable at a plurality ofpower levels and said driver is configured to selectively operate eachprimary inductive coil at a low power until the primary inductive coilclosest to said secondary inductive coil is identified and then tooperate said primary inductive coil closest to said secondary inductivecoil at a high power.

A second aspect of the invention is directed to an efficiency monitorfor monitoring the efficiency of said power transfer comprising thesignal transfer system described hereinabove; the efficiency monitorfurther comprising: at least one input power monitor for measuring theinput power delivered to said primary inductive coil; at least oneoutput power monitor for measuring the output power received by saidsecondary inductive coil; at least one processor for determining anindex of power-loss, and at least one communication channel forcommunicating said input power and said output power to said processor.

Typically, the efficiency monitor is further characterized by at leastone of the following restrictions:

-   -   the efficiency monitor additionally comprises at least one        circuit-breaker for disconnecting said primary inductive coil        from said power supply;    -   the input power monitor is incorporated into an inductive power        outlet;    -   the output power monitor is incorporated into an electric        device;    -   the index of power-loss is an efficiency quotient Q, defined as        the ratio of said output power to said input power;    -   the index of power-loss is an efficiency differential Δ, defined        as the difference between said output power and said input        power, and the efficiency monitor additionally comprises hazard        detectors in communication with said processor.

Optionally, the efficiency monitor is incorporated into an electricdevice that further comprises at least one said transmitter fortransmitting said output power to said receiver.

Optionally, the transmitter is selected from the group comprising: lightemitting diodes, radio transmitters, optocouplers, mechanicaloscillators, audio sources, ultrasonic transducers and ancillary loadtransmission circuits.

The signal transfer system may be incorporated into a power outletlocator for locating an inductive power outlet, said power outletcomprising at least one said primary inductive coil and at least onesaid transmitter; the system further comprising:

-   -   at least one sensor for detecting said control signal;    -   at least one processor for receiving a sensor signal from said        at least one sensor and computing at least one coordinate of a        location of said power outlet, and at least one user interface        for receiving a signal from said processor and communicating        said location to a user.

Typically, the power outlet locator is further characterized by at leastone of the following restrictions:

-   -   the at least one sensor being selected to detect an        electromagnetic field generated by at least one said primary        inductive coil;    -   the processor calculates the distance between said sensor and        said power outlet by comparing the intensity of said control        signal received by the sensor with a reference value;    -   the processor determines the direction of said power outlet by        comparing the relative intensities of said control signal as        detected by a plurality of said sensors;    -   the location of said power outlet being encoded into said        control signal and decoded by said processor;    -   the user interface comprises a visual display for indicating the        location of said power outlet, and        the user interface comprises an audible signal.

In one embodiment, the power outlet locator is incorporated into anelectrical device.

Optionally, the electrical device is further characterized by at leastone of the following restrictions:

-   -   the electrical device additionally comprises at least one said        secondary inductive coil for powering said electrical device;    -   the electrical device additionally comprises at least one        electrochemical power cell for powering said electrical device        and at least one said secondary inductive coil wired to said        electrochemical cell via a rectifier for charging said        electrochemical power cell, and        the electrical device is selected from the group comprising:        telephones, personal digital assistants (PDAs), cameras, media        players, computers, keyboards and cursor controllers.

A further aspect of the invention is directed to providing a method fortransmitting a control signal through an inductive energy couplingcomprising a primary inductive coil connected to a power source and asecondary inductive coil connected to an electric load, said methodcomprising:

-   -   providing an input signal;    -   providing a bit-rate signal;    -   modulating the bit-rate signal with the input signal to create a        modulated signal;    -   connecting an ancillary load to said secondary inductive coil        intermittently according to said modulated signal;    -   monitoring a primary current drawn by said primary inductive        coil and producing a primary current signal, and        cross-correlating said primary current signal with said bit-rate        signal to generate an output signal.

A further aspect of the invention is directed to providing a method formonitoring the efficiency of power transmission by an inductive poweroutlet comprising at least one primary inductive coil wired to a powersupply for inductively coupling with a secondary inductive coil wired toan electric device, said method comprising the steps of:

-   -   measuring the input power delivered to said primary inductive        coil;    -   measuring the output power received by said electric device;    -   communicating said input power to a processor;    -   communicating said output power to said processor, and said        processor determining an index of power-loss.

In one specific method, a working range of values for said index ofpower-loss is predetermined, and the method comprises the further stepof: disconnecting said primary inductive coil from said power supply ifsaid index of power-loss falls outside said working range of values.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the invention and to show how it may becarried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention; the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawings:

FIG. 1 is a block diagram showing the main elements of an inductivepower coupling incorporating a signal transfer system according to afirst embodiment of the invention;

FIG. 2 a-d show another embodiment of the signal transfer system inwhich a control signal is transmitted through an inductive energycoupling;

FIG. 3 is a schematic diagram showing a signal transfer systemintegrated into a contactless inductive power coupling system forpowering a computer;

FIG. 4 is a flowchart showing a method for transferring a transmissionsignal through an inductive energy coupling in accordance with theinvention.

FIG. 5 is a block diagram representing another embodiment of the signaltransfer system incorporated into an efficiency monitor for monitoringthe efficiency of power transmission by an inductive power outlet;

FIG. 6 a is a schematic diagram of an inductive power outlet with anelectrical load inductively coupled thereto, monitored by an efficiencymonitor;

FIG. 6 b is a schematic diagram of the inductive power outlet of FIG. 6a wherein a power drain has been introduced between the primary andsecondary coils;

FIG. 7 is a flow diagram of a method for using the signal transfersystem to monitor the efficiency of power transmission by an inductivepower outlet;

FIG. 8 a is a schematic representation of another embodiment of thesignal transfer system incorporated into a power outlet locator used toindicate the location of an inductive power outlet concealed behind asurface;

FIG. 8 b is a schematic representation of a computer standing on thesurface of FIG. 8 a and being powered by the concealed primary outlet;

FIG. 9 is a block diagram representing the main features of the poweroutlet locator;

FIG. 10 is a schematic representation of a power outlet locator withfour sensors;

FIG. 11 is a block diagram representing a power outlet locatorconfigured to receive and decode a control signal transmitted by a poweroutlet using still another embodiment of the signal transfer system;

FIG. 12 a-c are schematic representations of a mobile phoneincorporating a power outlet locator, wherein a graphical user interfacerepresents a virtual target superimposed over an image of the surface,and

FIG. 13 is a schematic representation of a signal transfer systemincorporated into a system for locating secondary coils placed upon amulti-coil power transmission surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made to FIG. 1 showing a block diagram of the mainelements of an inductive power coupling 200 incorporating a signaltransfer system 100 according to a first embodiment of the invention.

The inductive power coupling 200 consists of a primary inductive coil220 and a secondary inductive coil 260. The primary coil 220 is wired toa power supply 240 typically via a driver 230 which provides theelectronics necessary to drive the primary coil 220. Driving electronicsmay include a switching unit providing a high frequency oscillatingvoltage supply, for example. The secondary coil 260 is wired to anelectric load 280.

When the secondary coil 260 is brought into proximity with the primarycoil 220, the pair of coils forms an inductive couple and power istransferred from the primary coil 220 to the secondary coil 260. In thisway a power outlet 210 may provide power to an electric device 290.

The signal transfer system 100 comprises: a signal generator 120, forgenerating a control signal S_(C); a transmitter 140 for transmittingsaid control signal S_(C); and a receiver 160 for receiving said controlsignal S_(C).

Although in the signal transfer system 100 described herein, thetransmitter 140 is incorporated into the power outlet 210 and thereceiver 160 is incorporated into the electrical device 290, it will beappreciated that a transmitter 140 may alternatively or additionally beincorporated into the electrical device 290 and a receiver 160 mayalternatively or additionally be incorporated into the power outlet 210.

The control signal S_(C) communicates encoded data pertaining to thepower transmission. This data may be pertinent to regulating efficientpower transmission. Examples of such data includes parameters such as:required operating voltage, current, temperature or power for theelectric load 280, the measured voltage, current, temperature or powersupplied to the electric load 280 during operation, the measuredvoltage, current, temperature or power received by the electric load 280during operation and the like.

In other embodiments, the control signal S_(C) may communicate datarelating to the coordinates of the primary inductive coil 220 for thepurposes of indicating the location of the power outlet 210.Alternatively, the control signal S_(C) may communicate data relating tothe identity or presence of the electric load 280 such as the locationof the secondary coil 260, or an identification code or the electricdevice 290 or its user.

Various transmitters 140 and receivers 160 may be used with the signaltransfer system. Where the primary and secondary coils 220, 260 aregalvanically isolated for example, optocouplers may have a lightemitting diode serving as a transmitter 140 which sends encoded opticalsignals over short distances to a photo-transistor which serves as areceiver 160. Optocouplers typically need to be aligned such that thereis a line-of-sight between transmitter and receiver. In systems wherealignment between the transmitter 140 and receiver 160 may beproblematic, optocoupling may be inappropriate and alternative systemsmay be preferred such as ultrasonic signals transmitted by piezoelectricelements or radio signals such as Bluetooth, WiFi and the like.Alternatively the primary and secondary coils 220, 260 may themselvesserve as the transmitter 140 and receiver 160.

Coil-to-coil Signal Transfer

One aspect of the present embodiments relate to a signal transfer systemfor transferring a transmission signal regarding an electric loadconnectable via an inductive energy coupling to a power source. Theinductive energy coupling comprises a primary coil connectable to thepower source in inductive alignment with a secondary coil connectable tothe electric load, the system comprises at least one ancillary load; atleast one switching unit comprising a modulator for modulating abit-rate signal with an input signal to create a modulated signal and aswitch for intermittently connecting the ancillary load to the secondarycoil according to the modulated signal; at least one current monitor formonitoring primary current drawn by the primary coil and producing aprimary current signal, and at least one correlator forcross-correlating the primary current signal with the bit-rate signalfor producing an output signal.

The switching unit preferably also comprises a controller configured toencode data into the input signal. Typically, the switching unit furthercomprises a frequency divider and the inductive energy couplingtransfers energy with a driving frequency and the bit rate frequency isan integer fraction of the driving frequency.

The inductive energy coupling is typically a device wherein the primarycoil is galvanically isolated from said secondary coil. The device mayinclude a transformer, a DC-to-DC converter, an AC-to-DC converter, anAC-to-AC converter, a flyback transformer, a flyback converter, afull-bridge converter, a half-bridge converter, a buck converter, aboost converter, a buck-boost converter, a SEPIC converter or a zetaconverter, for example.

Optionally, the input signal carries encoded data pertaining to, forexample, the presence of the electric load, required operating voltagefor the electric load, required operating current for the electric load,required operating temperature for the electric load, measured operatingvoltage for the electric load, measured operating current for theelectric load, measured operating temperature for the electric load,and/or a user identification code.

In one embodiment, a contactless inductive coupling is provided,comprising the signal transfer system wherein the primary coil isembedded in a power jack and the secondary coil is embedded in a powerplug galvanically isolated from the power jack.

An aspect of the technology described herein, teaches a method fortransferring a signal through an inductive energy coupling, wherein theinductive energy coupling comprises a primary coil connected to a powersource and a secondary coil connected to an electric load, the methodcomprising the following steps: providing an input signal, providing abit-rate signal, modulating the bit-rate signal with the input signal tocreate a modulated signal, connecting an ancillary load to the secondarycoil intermittently according to the modulated signal, monitoring aprimary current drawn by the primary coil and producing a primarycurrent signal; and cross-correlating the primary current signal withthe bit-rate signal to generate an output signal.

According to another aspect, a method for regulating power transferacross a contactless inductive coupling is taught wherein the outputsignal provides details of power requirements of the load. Typically theinput signal is provided by encoding data regarding at least one powerrequirement of the electric load into the input signal. Optionally andtypically, the power requirement depends on parameters such as operatingvoltage, operating current and/or operating temperature. Alternativelythe input signal is provided by monitoring at least one operatingparameter of the electric load and encoding monitored parameter datainto the input signal. Optionally the parameter is selected from thegroup comprising operating voltage, operating current and operatingtemperature. Typically the method for transferring a signal through aninductive energy coupling includes a preliminary step of detecting thepresence of an electric load.

Reference is now made to FIGS. 2 a-d wherein a signal transfer system2100 according to a second general embodiment of the invention is shown.With particular reference to FIG. 2 a, the signal transfer system 2100is configured to transmit a transmission signal through an inductiveenergy coupling 2200. The inductive energy coupling 2200 consists of aprimary coil L₁ which may be connected to a power source 2240 and asecondary coil L₂, galvanically isolated therefrom, across which anelectric load 2280 may be connected either directly or via an AC-DCconverter 2270.

A transmission circuit 2140 may be connected in parallel with theelectric load 2280. The transmission circuit 2140 comprises an ancillaryload 2142 connected to the secondary coil L₂ via a switching unit 2144.Typically the ancillary load 2142 is much smaller than the electric load2280.

A corresponding reception circuit 2160 is connected to the primary coilL₁ of the inductive energy coupling 2200 and comprises a current monitor2162, such as an ammeter in series with the primary coil L₁, and acorrelator 2164.

The switching unit 2144 is configured to receive an input signal S_(in)and a bit-rate signal F_(b). A modulator (not shown) modulates thebit-rate signal F_(b) with the input signal S_(in) to produce amodulated signal S_(M). The ancillary load 2142 is intermittentlyconnected to the secondary coil L₂ at a rate determined by the modulatedsignal S_(M).

The power source 2240, such as an alternating-current voltage source,intermittent direct current voltage source or the like, is configuredand operable to produce a primary voltage V₁ which oscillates at adriving frequency F_(d). The oscillating primary voltage V₁ in coil L₁induces a secondary voltage V₂(t) in the secondary coil L₂. Thesecondary voltage V₂(t) is optionally passed through an AC-DC converter22 producing a direct-current voltage V₂₂(t).

The electric load 2280 which is coupled to the secondary coil L₂—eitherdirectly or via the AC-DC converter 2270-draws a load current I₂₂. Thepower P₂₂ provided to the load 2280 is given by the scalar product ofthe voltage V₂₂ and the load current I₂₂. When the ancillary load 2144is connected, an additional ancillary current i₂₄ is also drawn. Thus,with the ancillary load 2144 connected, the total power P₂ drawn by thesecondary coil L₂ is given by:

P ₂(t)={right arrow over (V)} ₂₂(t)[{right arrow over (I)} ₂₂ +{rightarrow over (i)} ₂₄(t)]

where the ancillary current signal i₂₄(t) varies with the modulatedsignal S_(M).

The input power P₁(t) provided to the primary coil L₁ is given by:

P ₁(t)={right arrow over (V)} ₁(t){right arrow over (I)} ₁₀(t)

where the primary voltage V₁(t) oscillates at the driving frequencyF_(d) which is determined by the power supply 2240.

Input power P₁(t) provided by the primary coil L₁ is generallyproportional to the total power P₂₂(t) drawn by the secondary coil L₂,and the primary voltage V₁(t) is determined by the power supply.Perturbations in the primary current I₁₀(t) supplied to the primary coilL₁ are thus in proportion with i₂₄(t).

The current monitor 2162 monitors the primary current I₁₀ (t) over time,producing a primary current signal S_(p) which typically has similarcharacteristics to the modulated signal S_(M). The correlator 2164 isconfigured to cross-correlate the primary current signal S_(p) with thebit rate F_(b). The output signal S_(out) of the correlator 2164therefore has the same characteristics as the input signal S_(in).

In this manner, information carried by the input signal S_(in) istransmitted from the transmission circuit 2140 and is retrievable by thereceiver circuit 2160 from the output signal S_(out). It is noted thatthe signal transfer system 2100 described herein, transmits atransmission signal across the same inductive power coupling 2200 asused for power transmission. This is in contradistinction to prior arttransmission systems, which use additional elements to provide signaltransmission channels separate from the power transmission channels. Inconsequence of this innovative approach, additional transmissionelements such as optocouplers, piezoelectric elements, supplementarycoil pairs and the like are not generally required.

With reference now to FIG. 2 b, an exemplary transmission circuit 2140of the signal transfer system 2100 of FIG. 2 a is shown. An AC-to-DCconverter 2270 comprising a diode 2272 and a capacitor 2274, which isconnected in parallel to the secondary coil L₂, converts an AC secondaryvoltage V₂ from the secondary coil L₂ into a DC load voltage V₂₂ whichis connected across an electric load 2280.

The connection between the ancillary load 2142 and the load voltage V₂is controlled by a switching unit 2144 which includes a frequencydivider 2145, microcontroller 2146 and a switch 2147. The frequencydivider 2145 provides the bit-rate signal F_(b) which is passed to themicrocontroller 2146. The microcontroller 2146 is configured to modulatethe bit-rate signal F_(b) according to input signals including controlsignals S_(c) from the electric load 2280 and external signals S_(E) asdescribed hereinbelow.

Control signals S_(c) may be used to regulate the power supply. Controlsignals S_(c) typically provide data relating to load parameters.Typically these include the required operating voltage, current andtemperature and the actual measured operating voltage, current andtemperature as monitored during operation of the load.

External Signals S_(E) may be used to provide the transmission circuit2140 with external data to be digitally encoded into the input signalS_(in) by the microcontroller 2146 and transmitted to the receivercircuit 2160. External information, may, for example, provide usefulsupplementary data such as a user identification code, a pass key,battery level of the load device and the like.

It will be appreciated that the ability to transmit supplementaryinformation such as external signals S_(E) through the inductive energycoupling 2200 presents a further advantage over prior art systems whichare only suitable for transmitting control signals.

FIG. 2 c shows a schematic representation of an exemplary receivercircuit 2160 in accordance with the signal transfer system of FIG. 2 a,consisting of a current monitor 2162, a frequency divider 2166, acorrelator 2164 and a microcontroller 2168. The frequency divider 2166provides the bit-rate signal F_(b) which is typically an integerfraction of the driving frequency F_(d). The current monitor 2162provides a primary current signal S_(p) which is passed to thecorrelator 2164 for cross-correlatation with the bit-rate signal F_(b).The resulting output signal S_(out) is passed to a microcontroller 2168which may use the output signal S_(out) to pass a control signal S_(C)to control the power source 2240 so as to regulate the power provided tothe electric load 2280. The microcontroller 2168 may also be used toextract external signals S_(E) from the output signal.

An exemplary use of the receiver circuit 2160 of FIG. 2 c is highlightedin FIG. 2 d which shows the receiver circuit 2160 configured to controla flyback power source 2240F. In a flyback converter, a direct currentvoltage source 2242 is intermittently connected to a primary coil L₁ bya switch 2244. This produces a varying voltage signal V₁(t) in theprimary coil L₁ which induces a secondary voltage V₂ in a secondary coilL₂ (FIG. 2 a). The secondary coil L₂ is generally connected to asmoothing circuit such the AC-DC converter 2270 shown in FIG. 2 b toproduce a DC output.

The switch 2244 is controlled by a driver 2248 which receives a pulsingsignal F_(d) from a clock 2246. The pulsing signal F_(d) determines thefrequency with which the direct current voltage source 2242 is connectedto the primary coil L₁. The power delivered to the primary coil L₁ maybe regulated by varying the duty cycle of the switch 2244. The dutycycle is the proportion of the time between pulses during which theswitch 2244 is closed.

FIG. 2 d shows the innovative use of the signal transfer system 2100which receives a feedback signal transferred between the primary andsecondary power transmission coils and received by the receiver circuit2160. This is an improvement on prior art flyback converters, whereinadditional elements such as optocouplers or the like have been used totransmit feedback signals.

The microcontroller 2168 generates a control signal S_(c) which isrelayed to the driver 2248. The control signal S_(c) determines the dutycycle of the switch 2248 and so may be used to regulate powertransmission.

Although only a flyback converter is represented in FIG. 2 d it is notedthat a control signal S_(c) thus transmitted may be used to regulatepower transfer in a variety of transmission assemblies such as atransformer, a DC-to-DC converter, an AC-to-DC converter, an AC-to-ACconverter, a flyback transformer, a full-bridge converter, a half-bridgeconverter or a forward converter for example.

As an example of the signal transfer system 100 (FIG. 1), with referenceto FIG. 3, according to a third embodiment of the invention, a signaltransfer system 3100 may be integrated into a contactless inductivepower coupling system 3200 where power is inductively transmitted from ajack unit 3212 to a plug unit 3292 galvanically isolated therefrom. Atransmission circuit 3140 embedded in the plug unit 3292 may be used totransmit control signals S_(c) to a receiver circuit 3160 in the jack3212. Thus once the primary L₁ and secondary L₂ coils are aligned,control signals may be passed between the plug 3292 and jack 3212 unitswith no need to align additional components such as optocouplers, andthe like.

Where a contactless plug 3292 is used, for example to power a portablecomputer 3290 having on-board power cells 3280, the signal transfersystem 3100 may be used to detect the presence of the load 3290producing a detection signal S_(DL) and then to provide the jack 3212with signals relating to the identity of the user S_(D) and the serialnumber S_(SN) or other identifier of the laptop computer 3290. Signalsregarding the operating voltage and current required by the PC may beprovided as a regulatory signal S_(Q) which may also providesupplementary information such as information related to the power levelof the cells 3280, for example. Using this signal S_(Q), the signaltransfer system 3100 may be used to select between powering the computer3290 directly, recharging the power cells 3280 thereof, or both poweringand recharging, depending on defaults and predetermined criteria. It isfurther noted that when used for recharging cells 3280, the ability tomonitor the temperature of the cells 3280 during recharging may be usedto prevent overheating.

Referring to FIG. 4, a flowchart showing a method for transferring atransmission signal through an inductive energy coupling in accordancewith another embodiment of the invention is presented. With furtherreference to FIG. 2 a, an Input Signal S_(in)-Step (a) and a Bit-rateSignal F_(b)-Step (b) are provided to the transmission circuit 2140. TheBit-rate Signal F_(b) is then modulated by the Input Signal S_(in),producing a Modulated Signal S_(M)-Step (c). An ancillary load 2142 isthen connected to the second coil L₂ intermittently according to theModulated Signal S_(M)-Step (e). The receiver circuit 2160 monitors theprimary current drawn by the primary coil L₁ to produce a PrimaryCurrent Signal S_(p)-Step (e). This Primary Current Signal S_(p) is thencross-correlated with the Bit-rate Signal F_(b) to generate an OutputSignal S_(out)-Step (f).

The basic signal transfer system and method described hereinabove arecapable of variation. For example, it will be appreciated that throughthe use of such a system, information regarding a load 2280 may betransmitted to the power outlet 2210 across the inductor coils L₁ and L₂of the inductive coupling 2200, as a signal superimposed on the powertransmitted, without requiring additional data transmitting components.

Power Coupling Efficiency

Embodiments of the invention are directed to providing methods formonitoring the efficiency of power transmission by an inductive poweroutlet comprising at least one primary coil wired to a power supply, forinductively coupling with a secondary coil wired to an electric device.The method comprises the steps of: measuring the input power deliveredto the primary coil, measuring the output power received by the electricdevice, communicating the input power to a processor, communicating theoutput power to the processor and the processor determining an index ofpower-loss.

In one specific application, the index of power-loss is an efficiencyquotient Q, being the ratio of the output power to the input power, andthe method comprises the further step of: disconnecting the primary coilfrom the power supply if the efficiency quotient Q is below a thresholdvalue. Typically the threshold efficiency quotient is in the range offrom 75% to 95%.

In another application, the index of power-loss is an efficiencydifferential Δ, being the difference between the output power to theinput power, and the method comprises the further step of: disconnectingthe primary coil from the power supply if the efficiency differential Δis above a threshold value.

A further aspect of the technology described herein relates to anefficiency monitor for monitoring the efficiency of power transmissionby an inductive power outlet of the type including at least one primarycoil wired to a power supply, for inductively coupling with a secondarycoil wired to an electric device. The efficiency monitor includes: atleast one input power monitor for measuring the input power delivered tothe primary coil; at least one output power monitor for measuring theoutput power received by the secondary coil; at least one processor fordetermining an index of power-loss; and at least one communicationchannel for communicating the input power and the output power to theprocessor.

Typically the efficiency monitor also includes at least onecircuit-breaker for disconnecting the primary coil from the powersupply. Preferably the input power monitor is incorporated within thepower outlet and the output power monitor is incorporated within theelectric device.

Optionally, the electric device comprises at least one transmitter fortransmitting the output power to a receiver incorporated in the poweroutlet. The transmitter may include one or more light emitting diodes,radio transmitters, optocouplers, or ancillary load transmittercircuits, for example.

According to preferred embodiments, the efficiency monitor includes oneor more hazard detectors in communication with the processor. Suchhazard detectors may include magnetic sensors, heat sensors,electromagnetic radiation sensors and Hall probes, for example.

Reference is now made to FIG. 5 showing a block diagram of a signaltransfer system 4100. The signal transfer system 4100 is incorporatedinto an efficiency monitor 4300 for monitoring the efficiency of powertransmission by an inductive power outlet 4210.

The inductive power outlet 4210 consists of a primary coil 4220 wired toa power supply 4240 via a driver 4230 which provides the electronicsnecessary to drive the primary coil 4220. Driving electronics mayinclude a switching unit providing a high frequency oscillating voltagesupply, for example.

If a secondary coil 4260 is brought into proximity with the primary coil4220, the pair of coils forms an inductive couple, and power istransferred from the primary coil 4220 to the secondary coil 4260. Inthis way the power outlet 4210 may provide power to an electric device4262 comprising an electric load 4280 wired in series with the secondarycoil 4260.

The efficiency monitor 4300 consists of an input power monitor 4122incorporated within the power outlet 4210 and an output power monitor4124 incorporated within the electric device 4290, both in communicationwith a processor 4162.

The input power monitor 4122 is configured to measure the input powerprovided by the primary coil 4220 and communicates this value to theprocessor 4162. The output power monitor 4124 is configured to measurethe output power P_(out) received by the secondary coil 4260 andcommunicates this value to the processor 4162.

The processor 4162 is configured to receive the values of the inputpower P_(in) and the output power P_(out) and to calculate an index ofpower-loss. The index of power loss indicates how much power is leakingfrom the inductive couple. The index of power-loss may be the efficiencyquotient Q which is the ratio between them, P_(out)/P_(in), which is anindication of the efficiency of the inductive coupling. Alternativelythe index of power loss may be the efficiency differential Δ which isthe difference between P_(out) and P_(in).

The processor 4162 may additionally or alternatively be configured totrigger a circuit-breaker 4280 thereby cutting off the primary coil 4220from the power supply 4240 when the efficiency quotient Q falls below apredetermined threshold or the efficiency differential Δ rises above apredetermined threshold. Typically, this predetermined threshold for theefficiency quotient Q is in the range of from about 75% to 95%, and morepreferably about 85%.

With reference to FIG. 6 a, an efficiency monitor 5300 for an inductivepower outlet 5210 is shown. Inductive power outlet 5210 consists of aprimary coil 5220 wired to a power source 5240 via an efficiency monitor5300 all concealed behind a facing layer 5642 of a horizontal platform5640 such as a desk-top, a kitchen work-top, a conference table or awork bench. The facing layer may be a sheet of self-adhesive plasticfilm, plastic, vinyl, Formica or wood veneer, for example.

In other embodiments a primary coil 5220 may be concealed beneath orwithin flooring such as rugs, fitted carpet, parquet, linoleum, floortiles, tiling, paving and the like. Alternatively the primary coil 5220may be concealed behind or within a vertical surface such as a wall of abuilding or a cabinet, for example behind wallpaper or stretched canvasor the like.

The primary coil 5220 may be used to power an electrical device 5290such as a computer wired to a secondary coil 5260. The electrical device5290 is placed upon the surface 5642 of a platform 5640 such that thesecondary coil 5260 is aligned with the primary coil 5220 therebeneath.

The efficiency of the power outlet 5210 is monitored by an efficiencymonitor 5300. An input power monitor 5122 is incorporated within thepower outlet 5210 behind the platform 5640 and is in direct conductivecommunication with a processor 5162. An output power monitor 5124 isincorporated within the electrical device 5290 and is not physicallyconnected to the power outlet 5210. The output power monitor 5124communicates with the processor 5162 via a signal transfer system 5100comprising a transmitter 5140 incorporated within the electrical device5290 which is configured to transmit a signal to a receiver 5160incorporated within the power outlet 5210.

The transmitter 5140 may be a standard transmitter such as those widelyused in computing and telecommunications, such as an Infra-red, Wi-fi orBluetooth transmitter or the like. Indeed, any light emitting diodes,radio transmitters, optocouplers or other such transmitters of radiationfor which the platform 5640 is translucent may be used. Alternatively afiber optic pathway may be provided through the platform.

In certain embodiments, an optical transmitter, such as a light emittingdiode (LED) for example, is incorporated within the power outlet 5210and is configured and operable to transmit electromagnetic radiation ofa type and intensity capable of penetrating the casing of the electricaldevice 5290, and the surface layer 5642. An optical receiver, such as aphotodiode, a phototransistor, a light dependent resistors of the like,is incorporated within the primary unit for receiving theelectromagnetic radiation transmitted through the surface layer 5642.

It is noted that many materials are partially translucent to infra-redlight. It has been found that relatively low intensity infra red signalsfrom LEDs and the like, penetrate several hundred microns of commonmaterials such as plastic, cardboard, Formica or paper sheet, to asufficient degree that an optical receiver, such as a photodiode, aphototransistor, a light dependent resistors or the like, behind a sheetof from 0.1 mm to 2 mm of such materials, can receive and process thesignal. For example a signal from an Avago HSDL-4420 LED transmitting at850 nm over 24 degrees, may be detected by an Everlight PD15-22C-TR8 NPNphotodiode, from behind a 0.8 mm Formica sheet. For signalling purposes,a high degree of attenuation may be tolerated, and penetration of only asmall fraction, say 0.1% of the transmitted signal intensity may besufficient. Thus an infra-red signal may be used to provide acommunication channel between primary and secondary units galvanicallyisolated from each other by a few hundred microns of wood, plastic,Formica, wood veneer, glass or the like.

The transmitter 5140 and receiver 5160 may be laterally displaced fromthe primary coil 5220 and secondary coil 5260. In preferred embodiments,however, the transmitter 5140 is located at the center of the secondarycoil 5260 and the receiver 5160 is located at the center of the primarycoil 5220. This permits alignment to be maintained through 360 degreerotation of the secondary coil 5260 relative to the primary coil 5220.

The processor 5162 is configured to receive the values of the inputpower P_(in), directly from the input power monitor 5122, and the outputpower P_(out), via the receiver 5160. The processor 5162 then calculatesthe efficiency quotient Q. In normal usage as represented in FIG. 6 a,the processor records an efficiency quotient Q higher than apredetermined threshold so power transmission continues uninterrupted.When the efficiency quotient Q falls below a predetermined threshold,this indicates that power is being drawn from the primary coil 5220 bysome power drain other than the secondary coil 5260.

FIG. 6 b is a schematic diagram of the inductive power outlet 5210 ofFIG. 6 a wherein a power drain such as a conductive sheet of metallicfoil 5800 is introduced between the primary coil 5220 and the secondarycoil 5260. The oscillating magnetic field produced by the primary coil5220 when connected to a high frequency oscillating voltage from adriver 5230, produces eddy currents in the conductive sheet 5800 therebyheating the conductive sheet and draining power from the primary coil5220. Such a power drain may be wasteful and/or dangerous. It will beappreciated that leak prevention systems which cut off power to theprimary coil 5220 if no secondary coil 5260 is coupled thereto, wouldfail to detect this hazard.

In contradistinction to previous systems known to the inventors,embodiments of the present invention measure the efficiency quotient Q.Consequently, when a power drain is introduced, such as that shown inFIG. 6 b, for example, the output power P_(out) received by thesecondary coil 5260 is lower than normal and the efficiency quotient Qmay therefore drop below the predetermined threshold. The efficiencymonitor 5300 is thus able to detect the hazard.

According to certain embodiments, additional detectors (not shown) maybe incorporated within the power outlet 5210, the platform 5640 or theelectrical device 5290 for monitoring other scientific effects which maybe indications of possible hazards such as the magnetic field generatedby the primary coil 5220, or the temperature of the platform 5640 forexample. Such detectors may function in accordance with one or more of avariety of principles, including, inter alia, magnetic sensing means,Hall probes, heat sensors or electromagnetic sensors.

The processor 5162 may assess the level of the hazard detected byprocessing the various signals received according to a predeterminedlogical sequence. If necessary, the processor 5162 may trigger acircuit-breaker 5280 thereby cutting off the primary coil 5220 from thepower supply 5240. Depending on the nature of the hazard, the processor5162 may additionally or alternatively alert a user to the hazard. Thealert may be a visual or audio alarm for example, such as a buzzer orlight incorporated in the power transmission surface, or a signal sentto the computer 5290 which displays a warning 5294 on its visual display5296 or emits a warning sound.

In preferred embodiments the output power P_(out) may be monitored andencoded into the input signal S_(in). The coil-to-coil signal generatorshown in FIG. 2 a may be used to transmit the input signal S_(in) from atransmission circuit 2140 (FIG. 2 a) incorporated within an electricaldevice 290 (FIG. 1) and is retrievable by the receiver circuit 2160(FIG. 2 a) incorporated within the power outlet 210 (FIG. 1) from theoutput signal S_(out). The retrieved signal may then be communicated toa processor which uses it to calculate the efficiency quotient Q.

Reference is now made to FIG. 7 showing a flow diagram of a method formonitoring the efficiency of power transmission by an inductive poweroutlet according to a further embodiment of the present invention. Themethod includes the following steps:

-   -   a) measuring the input power delivered to a primary coil;    -   b) measuring the output power received by an electric device;    -   c) communicating the input power to a processor;    -   d) communicating the output power P_(out) to the processor;    -   e) determining an index of power-loss, such as an efficiency        quotient Q or efficiency differential Δ;    -   f) optionally, disconnecting the primary coil from the power        supply, for example if the efficiency quotient Q is below a        threshold value (f1) or the efficiency differential Δ is above a        threshold value (f2), thereby preventing power leakage.

Primary Coil Locators

Another aspect of the invention is directed to providing a power outletlocator for locating an inductive power outlet of the type comprising atleast one primary coil wired to a power supply for inductively couplingwith a secondary coil wired to an electrical device. Typically, thepower outlet locator comprises at least one sensor for detecting the atleast one power outlet, at least one processor for receiving a sensorsignal from the at least one sensor and computing at least onecoordinate of a location of the at least one power outlet and at leastone user interface for receiving a signal from the processor andcommunicating the location to a user.

Preferably, at least one sensor is selected to detect radiationtransmitted by the at least one the power outlet. Typically, at leastone sensor is selected to detect an electromagnetic field generated byat least one the primary coil. Optionally the processor calculates thedistance between the sensor and the power outlet by comparing theintensity of the radiation received by the sensor with a referencevalue. Typically, the processor determines the direction to the poweroutlet by comparing the relative intensities of the radiation detectedby a plurality of the sensors. Alternatively the location of the poweroutlet is encoded into a signal transmitted by the power outlet anddecoded by the processor.

Typically, the user interface comprises a visual display. Optionally,the visual display indicates the direction of the power outlet.Preferably, the visual display indicates the distance to the poweroutlet. Preferably, the visual display comprises a graphical userinterface representing at least a section of a target comprisingconcentric rings centered on a point indicating the location of thepower outlet. Typically, the power outlet is concealed behind a surfaceand the target is superimposed upon an image of the surface.Alternatively or additionally, the user interface comprises an audiblesignal.

Another aspect of the invention is to provide an electrical deviceincorporating a power outlet locator. Typically, the electrical deviceadditionally comprises at least one secondary inductive coil forpowering the electrical device. Optionally, the electrical deviceadditionally comprises at least one electrochemical power cell forpowering the electrical device and at least one the secondary inductivecoil wired to the electrochemical cell via a rectifier for charging theelectrochemical power cell. The electrical device may be, but is notnecessarily, selected from the group comprising: telephones, personaldigital assistants (PDAs), cameras, media players, computers, keyboardsand mice.

Reference is now made to FIG. 8 a showing a schematic representation ofsuch a power outlet locator 6300 which utilizes such a signal transfersystem. The location of an inductive power outlet 6210, concealed behinda surface 6642, is indicated by an arrow 6362 displayed upon a visualuser interface 6360.

The inductive power outlet 6210 is wired to a power source typically viaa driver 230 (FIG. 1) providing the electronics necessary to drive theinductive power outlet 6210, such as a switching unit providing a highfrequency oscillating voltage supply, for example.

The inductive power outlet 6210 may be incorporated into a verticalsurface such as a wall of a building or a cabinet. The inductive poweroutlet 6210 may be concealed behind a surface 6642 of wallpaper orstretched canvas for example. Alternatively the inductive power outlet6210 may be incorporated behind a facing layer of a horizontal platformsuch as a desk-top, a kitchen work-top, a conference table or a workbench for example of mica, Formica or wood veneer. Alternatively, again,an inductive power outlet 6210 may be concealed beneath flooring such asrugs, fitted carpet, parquet, linoleum, floor tiles, tiling, paving andthe like.

It will be apparent that when the location of the inductive power outlet6210 is known, a secondary coil 6260 may be brought into alignmenttherewith, as shown in FIG. 8 b, for example. Thus with reference toFIG. 8 b, the inductive power outlet 6210 may inductively couple withthe secondary coil 6260 and thereby power an electrical device, such asa computer 6290, wired to the secondary coil 6260. It is noted thataccording to some embodiments, the electrical device, such as a computer6290 may itself incorporate an integral inductive power outlet locator.

With reference now to FIG. 9, a block diagram representing the mainfunctional components of a power outlet locator 7300 is shown. A sensingunit 7160 configured and operable to detect an inductive power outlet7210 is provided. A processor 7362, in communication with the sensingunit 7160, is configured to compute the location of the power outlet7210. A user interface 7360 is provided for communicating the computedlocation to a user.

According to various embodiments, the sensor unit 7160 may incorporatemagnetic sensors such as Hall probes, for example, configured to detectthe magnetic field generated by the inductive power outlet directly.Alternatively, the sensor unit 7160 may incorporate a radio receiver forreceiving a radio signal transmitted from the power outlet. It will beappreciated, however, that appropriate sensors may be selected fordetecting specific electromagnetic wavelengths, including ultra-violetradiation, micro waves, radio waves or even x-ray or shorterwavelengths. Furthermore, the sensing unit may be configured to receiveother types of radiation, including mechanical vibrations such as bothaudible and inaudible (e.g. ultrasonic) sound waves.

By way of example, an exemplary sensing unit 7460 is represented in FIG.10, four sensors 7462 a-d, such as proximity sensors based on volumesensors, infra-red sensors, ultrasonic sensors, magnetic sensors (likeHall probes), inductance sensors, capacitance sensors or the like, arearranged in a diamond configuration.

Each sensor 7462 is configured to receive a control signal S_(C)transmitted from an inductive power outlet 7210. The processor 7362 maycompare the intensity I of the control signal S_(c) detected by a sensor7462 with a reference value I_(r) to indicate the distance between thesensor 7462 and the power outlet 7210.

Furthermore, the diamond configuration, provides two perpendicularopposing pairs of sensors 7462 a-b, 7462 c-d. The intensity I of thecontrol signal S_(C) is measured by each sensor independently. Theprocessor 7460 may use the differences between intensities measured byopposing pairs (I_(a)-I_(b)), (I_(c)-I_(d)) to provide vectorcoordinates indicating the direction of the power outlet 7210. Althougha two dimensional vector is computed using the two dimensional diamondconfiguration of sensors described hereinabove, it will be appreciatedthat a three dimensional vector may be computed from three pairs ofsensors in a tetrahedral configuration.

It will be appreciated that the computation method herein described areby way of example, for illustrative purposes only. Alternative methodsby which the processor may compute the direction of the power outletwill be familiar to those skilled in the art.

FIG. 11 shows a block diagram representing a power outlet locator 8500in accordance with yet another embodiment. An inductive power outlet8210 transmits a control signal S_(C) which carries an encoded locationsignal S_(L) identifying the location of the inductive power outlet8210. A primary coil 8220 is connected to a power supply 8240 via aswitching unit 8232 and a microcontroller 8234. The switching unit 8232is configured to intermittently connect the power supply 8240 to theprimary coil 8220 with a bit-rate frequency f The location of theprimary coil 8220 is encoded into a location signal S_(L) which is sentto the microcontroller 8234. The microcontroller 8234 is configured tomodulate the bit-rate signal with the location signal S_(L).

The voltage applied to the primary coil 8220 is thus a modulatedvariable voltage with a frequency f, carrying an encoded location signalS_(L). It will be appreciated that the variable voltage may produce aradio wave of frequency f which may be transmitted as a control signalS_(C). Alternatively, the control signal S_(C) may be transmitted by adedicated transmitter separate from the primary coil 8220.

The power outlet locator 8500 includes a receiver 8160, a clock 8542 anda cross-correlator 8544. The radio receiver 8160 is tunable to receiveradio waves of frequency f, such that it may receive the control signalS_(C). The clock 8542 produces a fixed reference signal R of frequencyf. The cross-correlator 8544 receives both the reference signal R fromthe clock 8542 and the control signal S_(c) from the receiver 8160 andby cross-correlating these signals the location signal S_(L) isisolated.

Although a digital bit-rate modulated control signal S_(C) is describedhereinabove, it will be appreciated that the control signal S_(C) mayalternatively be modulated in other ways such as by analogue or digitalfrequency modulation or by amplitude modulation, for example.

The location of the power outlet 8210 may thereby be transmitted to aremote power outlet indicator 8500, which may then output the locationof the power outlet 8210 a user interface 7360 (FIG. 9).

As shown in FIGS. 12 a-c, a power outlet locator 9300 may beincorporated into a mobile phone 9290, for example, thereby providing aconvenient means of locating concealed inductive power outlets. Agraphical user interface 9360, displayed upon the visual display of themobile phone 9290, represents a virtual target 9660, centered upon thepower outlet (not shown) and superimposed over the surface 9640 behindwhich the power outlet is concealed.

Although the whole of the virtual target 9660 is represented by a dottedline in FIGS. 12 a-c for convenience, only the section 9661 a-c of thevirtual target 9660 in the visual display 9360 of the mobile phone 9290will normally be visible. The displayed section depends upon thelocation of the mobile phone 9290. Thus the curvature of the visibleconcentric arcs may indicate both the direction and distance to thepower outlet. It will be appreciated that the virtual target 9660 may bedisplayed upon a blank background or alternatively may be superimposedupon an image of the surface 9640, for example a real time imageproduced by the camera (not shown) of the mobile phone 9660.

It is further noted that the mobile phone 9290 may itself carry asecondary inductive coil (not shown) wired to a electrochemical cell viaa rectifier for inductively coupling with a inductive power outlet andcharging the electrochemical power cell. Optimal alignment between thesecondary coil and the inductive power outlet may additionally beindicated by an audible signal such as a ring-tone or the like. In otherembodiments, particularly useful for the visually impaired, an audiblesignal may be additionally or alternatively be provided to guide theuser to the power outlet, perhaps verbally or alternatively throughother variations in pitch, volume or timbre.

It will be apparent that in certain situations such as when the powersource of the mobile phone 9660 is completely devoid of power, a poweroutlet locator 9300 which draws power from the mobile phone 9290 isimpractical. In alternative embodiments, therefore, a power outletlocator may be an independently powered unit with a user interfaceseparate from that of the mobile phone 9290. For example, in anotherembodiment, the power outlet locator draws power from the secondaryinductive coil. Additionally or alternatively, it may include adedicated electrochemical power source, for example. The relativebrightness of four light emitting diodes mounted upon the corners of themobile phone may indicate both the direction and proximity to a primarycoil.

Whilst the power outlet locator 9300 is incorporated into a mobile phone9290 it is noted that such a power outlet locator may alternatively beincorporated within other electrical devices such as fixed telephones,personal digital assistants (PDAs), cameras, media players, computers,keyboards, cursor controllers (e.g. mice) and the like.

Secondary Coil Locators

The signal transfer system may be associated with the primary coil andused to detect the location of the secondary inductive coil. Forexample, in a power outlet surface comprising multiple primary coils,each primary coil may be independently connected to the power source viaa driver. The signal transfer system may be used to identify the primarycoil closest to the location of a secondary coil. Typically, the primarycoils may be driven at multiple power levels, such that a low powerlevel is used to locate the secondary coil and a higher power is used totransfer power when a secondary coil is located.

In preferred embodiments the secondary coil is wired to a transmissioncircuit comprising an ancillary load connectable to the secondary coilvia a half-wave rectifier, such as a diode. The transmission circuit mayalso comprise a smoothing capacitor, a low power current source and a DCto DC converter.

When in detection mode, the driver activates each primary coilsequentially at low power. When a secondary coil is close enough to aprimary coil to inductively couple with it, the low power pulse istransferred from the primary coil to the secondary coil. An AC voltageis induced in the secondary coil and the transmission circuit isactivated. A DC current is produced by the half-wave rectifier and flowsthrough the ancillary load.

A control signal is transmitted by the secondary coil due to thetransmission circuit. Because half-wave rectification is used, evenharmonics of the power transmission frequency are generated. These maybe detected by a reception circuit connected to the primary coil, forexample by cross-correlating the power transmission frequency with areference clock frequency.

The strength of the even harmonic signals may indicate the proximity ofthe primary to the secondary coil. Once a secondary coil is detected,the driver may switch the closest primary coil to power transmissionmode, typically at a higher power.

It will be appreciated that in applications where a main electric loadis itself wired to the secondary coil via an AC-DC power converter whichperforms half-wave rectification, even harmonics are produced wheneverthe secondary coil is coupled to a primary coil, whether or not theancillary load is connected. The strength and phase of both odd and evenharmonics may be continuously monitored during power transmission sothat if the secondary coil is displaced or removed it will be readilydetected. Optionally the transmission circuit may be deactivated whenpower is provided to the electric load. Alternatively, where the mainload is wired to the secondary coil via a half-wave rectifier, theancillary load may be dispensed with entirely.

FIG. 13 shows the signal transfer system 2101 according to yet anotherembodiment of the invention. The signal transfer system 2101 is used forlocating a secondary coil L₂₂ wired to an electric load 2281, which isplaced somewhere over a multi-coil power transmission surface 2211.

The multi-coil power transmission surface 2211 comprises an array ofprimary coils L_(1n) each connected to a driver 2231 wired to a powersource 2241. The signal transfer system 2101 includes a transmissioncircuit 2141 wired to the secondary coil 2221 and a reception circuit2161 connected to the driver 2231. The transmission circuit 2141includes a half-wave rectifier 2144 connected to an ancillary load 2142and the reception circuit 2161 is configured to detect second harmonicsignals in the power supplied to the primary inductive coil L_(1n) whenthe secondary inductive coil L₂₂ is coupled thereto.

The driver 2231 is configured to selectively operate each primaryinductive coil L_(1n) in turn preferably at low power so as to identifywhich primary inductive coil is closest to the secondary inductive coilL₂₂. When a secondary coil L₂₂ is detected, the driver 2231 is thenconfigured to operate the primary inductive coil L_(1n) closest to thesecondary inductive coil L₂₂ at a high power. It will be appreciatedthat for some purposes it may be desirable to disconnect thetransmission circuit 2141 after the secondary inductive coil L₂₂ iscoupled to a primary coil L_(1n).

Thus a number of related technologies are presented that use signaltransfer systems across an inductive power coupling to regulate thepower and to detect and align the two coils.

The scope of the present invention is defined by the appended claims andincludes both combinations and sub combinations of the various featuresdescribed hereinabove as well as variations and modifications thereof,which would occur to persons skilled in the art upon reading theforegoing description.

In the claims, the word “comprise”, and variations thereof such as“comprises”, “comprising” and the like indicate that the componentslisted are included, but not generally to the exclusion of othercomponents.

What is claimed is:
 1. An efficiency monitor for monitoring power transmission by an inductive power outlet, the inductive power outlet comprising at least one primary coil wired to a power supply, for inductively coupling with a secondary coil wired to an electric load, the efficiency monitor comprising: at least one input power monitor for measuring input power delivered to the primary coil; at least one output power monitor for measuring output power received by the secondary coil; at least one processor for determining an index of power-loss; and at least one communication channel for communicating the input power and the output power to the processor.
 2. The efficiency monitor of claim 1 additionally comprising at least one circuit-breaker configured to disconnect the primary coil from the power supply.
 3. The efficiency monitor of claim 1 wherein the input power monitor is incorporated into the inductive power outlet.
 4. The efficiency monitor of claim 1 wherein the output power monitor is incorporated into an inductive power receiver unit.
 5. The efficiency monitor of claim 4 wherein the inductive power receiver unit comprises at least one signal transmitter for transmitting a signal to a receiver incorporated in the power outlet, the signal carrying data pertaining to the output power.
 6. The efficiency monitor of claim 5 wherein the signal transmitter is selected from a group consisting of: light emitting diodes, radio transmitters, optocouplers, and transmitter circuits.
 7. The efficiency monitor of claim 5 wherein the transmitter comprises: an ancillary load selectively connectable to the secondary inductive coil, a modulator for modulating a bit-rate signal with an input signal to create a modulated signal, and a switch for intermittently connecting the ancillary load to the secondary inductive coil according to the modulated signal.
 8. The efficiency monitor of claim 1 additionally comprising hazard detectors in communication with the processor.
 9. The efficiency monitor of claim 8 wherein the hazard detectors are selected from a group consisting of: magnetic sensors, heat sensors, electromagnetic radiation sensors and Hall probes.
 10. The efficiency monitor of claim 1 wherein the index of power comprises at least one of: an efficiency quotient Q, defined as the ratio of the output power to the input power, and an efficiency differential Δ, defined as the difference between the output power and the input power.
 11. A method for monitoring the efficiency of power transmission by an inductive power outlet, the inductive power outlet comprising at least one primary coil wired to a power supply, for inductively coupling with a secondary coil wired to an electric load, the method comprising the steps of: q. measuring the input power delivered to the primary coil; r. measuring the output power received by the secondary coil; s. communicating the input power to a processor; t. communicating the output power to the processor; and u. the processor determining an index of power-loss.
 12. The method of claim 11, wherein the index of power-loss is an efficiency quotient Q, being the ratio of the output power to the input power, the method comprising the further step of: disconnecting the primary coil from the power supply if the efficiency quotient Q is below a threshold value.
 13. The method of claim 11, wherein the index of power-loss is the efficiency differential Δ, being the difference between the output power to the input power, the method comprising the further step of: disconnecting the primary coil from the power supply if the efficiency differential Δ is above a threshold value.
 14. An inductive power outlet comprising at least one primary coil, for inductively coupling with a secondary coil wired to an electric load, the inductive power outlet further comprising an efficiency monitor comprising: at least one input power monitor configured to measure input power delivered to the primary coil; at least one signal detector configured to detect signals carrying data pertaining to output power received by the secondary coil; at least one processor configured to receive data pertaining to the input power and the output power, the processor further configured to determine an index of power-loss.
 15. The inductive power outlet of claim 14 additionally comprising at least one circuit-breaker configured to disconnect the primary coil from the power supply.
 16. An inductive power receiver comprising at least one secondary coil for inductively coupling to a primary coil and supplying power to an electric load, the inductive power receiver further comprising at least one output power monitor for measuring output power received by the secondary coil, and at least one signal transmitter configured to transmit signals carrying data pertaining to the output power to an efficiency monitor.
 17. The inductive power receiver of claim 16 wherein the signal transmitter is selected from a group consisting of: light emitting diodes, radio transmitters, optocouplers, and transmitter circuits.
 18. The inductive power receiver of claim 16 wherein the transmitter comprises: an ancillary load selectively connectable to the secondary inductive coil, a modulator for modulating a bit-rate signal with an input signal to create a modulated signal, and a switch for intermittently connecting the ancillary load to the secondary inductive coil according to the modulated signal.
 19. The inductive power receiver of claim 16 wherein the output power monitor is incorporated into an electric device.
 20. The inductive power receiver of claim 19 wherein the electric device is selected from a group consisting of: computers, telephones, personal digital assistance (PDAs), cameras, media players, computers, keyboards and mice. 